meson: rename libbasic to libbasic_static

Our variables for internal libraries are named 'libfoo' for the shared lib
variant, and 'libfoo_static' for the static lib variant. The only exception was
libbasic, because we didn't have a shared variant for it. But let's rename it
for consitency. This makes the build config easier to understand.

src/basic/meson.build

@@ -274,7 +274,7 @@ filesystem_switch_case_h = custom_target(
 
 basic_sources += [filesystem_list_h, filesystem_switch_case_h, filesystems_gperf_h]
 
-libbasic = static_library(
+libbasic_static = static_library(
         'basic',
         basic_sources,
         fundamental_sources,